Herbs, unarmed, often reduced and/or monocaulous, often rhizomatous or tuberous, usually notably fleshy; stems flattened to subterete. Raphides present. Leaves opposite, apparently verticillate due to closely set stem nodes and/or leaflike stipules, or slightly to markedly anisophyllous and apparently alternate, decussate or distichous, without domatia; stipules persistent or deciduous, interpetiolar, entire or bilobed, sometimes leaflike and thus apparently absent. Inflorescences terminal or sometimes pseudoaxillary, fasciculate, cymose-corymbiform, or umbelliform, several flowered, few flowered, or reduced to 1 flower, sessile to pedunculate, bracteate with bracts sometimes fused into an involucre or sometimes with bracts very reduced. Flowers pedicellate or sessile, bisexual or monomorphic, sometimes somewhat zygomorphic, usually nodding. Calyx limb deeply 4- or 5-lobed. Corolla white, broadly rotate (i.e., "Solanum-like") to campanulate (i.e., bell-shaped), glabrous inside; lobes 4 or 5, valvate in bud. Stamens 4 or 5, inserted near base of corolla tube, partially to fully exserted; filaments reduced or developed and free, coherent, or fused in middle portions into a tube; anthers free or usually coherent into a tube, with longitudinal slits or terminal pores, sometimes with connective prolonged at apex. Ovary 2-celled, ovules numerous in each cell on axile placentas attached near top of septum; stigma capitate or 2-lobed, included or exserted. Fruiting pedicels usually becoming thickened and erect. Fruit capsular, subglobose to obovoid, dehiscent through apical operculum formed from disk portion, leathery or membranous, often becoming black, with calyx limb persistent, with endocarp and septum becoming notably fibrous; seeds numerous, small, flattened to angled, with testa reticulate; endosperm fleshy.

The morphology and anatomy of the androecium of Argostemma were detailed by Puff et al. (Ann. Missouri Bot. Gard. 82: 358-366. 1995), who noted an absence of nectaries and probable buzz-pollination of flowers with both linear and poricidal anther dehiscence. Bremer (Ann. Missouri Bot. Gard. 76: 7-49. 1989) reported that the inner layers of the fruit become fibrous and trap seeds inside, with some of them sprouting while still in the capsule in an unusual form of vivipary. Argostemma was studied in Thailand by Sridith (Thai Forest Bull., Bot. 27: 86-137. 1999) and Sridith and Puff (Thai Forest Bull., Bot. 28: 123-137. 2000). Argostemma species apparently vary widely in size of individual plants and vegetative organs probably in relation to environmental factors.